1. Field of the Invention
The present invention relates to a wheel support bearing assembly for, for example, a passenger car or freight vehicle, which is designed to have an increased strength.
2. Description of the Prior Art
In a wheel support bearing assembly of a kind to which the present invention pertains, it is well known that the wheel hub has a wheel mounting flange formed integrally therewith so as to extend radially outwardly therefrom so that a vehicle wheel can be removably secured thereto by means of a plurality of bolts. This wheel mounting flange has a root portion integral with the wheel hub, which generally tends to be subjected to considerable stresses particularly when an automotive vehicle makes an abrupt turn. Accordingly, in order to increase the fatigue strength for the purpose of avoiding fracture of the root portion of the wheel mounting flange relative to the wheel hub, such root portion is generally treated with an induction heat treatment such as disclosed in, for example, the Japanese Laid-open Patent Publication No. 2004-182127, published Jul. 2, 2004, or a shot peening such as disclosed in, for example, the Japanese Laid-open Patent Publication No. 2005-145313, published Jun. 9, 2005. Also, in order to increase the fatigue strength, a method has been suggested, in which a component part is in its entirety quenched and tempered such as disclosed in, for example, the Japanese Laid-open Patent Publication No. 2005-003061, published Jan. 6, 2005.
FIG. 82 illustrates a generally employed method of making a wheel hub used in a conventional wheel support bearing assembly of a third generation type. This generally employed method includes cutting a bar W0 to a predetermined size as shown by Process (A) in FIG. 82 to thereby provide a billet W1, as shown by Process (B) in FIG. 82, which eventually serves a raw material for one wheel hub. The billet W1 is then passed through a plurality of passes forming respective steps of a hot forging process, which passes include, for example, a first forging pass, a second forging pass and a third forging pass, to allow it to eventually assume a shape similar to the shape of the wheel hub, followed by a final forging process by which a finally forged product W4 of a shape approximately similar to the shape of the wheel hub can be obtained. See Process (C) to Process (E) in FIG. 82.
The finally forged product W4 is treated with a shot blasting for the purpose of removal of surface scales and is subsequently normalized or quenched and tempered if so required, as shown by Process (F) in FIG. 82. Then, the finally forged product W4 is subjected to turning as shown by Process (G) in FIG. 82, followed by induction heat treatment, as shown by Process (H) in FIG. 82, applied to raceways. Also, if required, a secondary machining is carried out subject to flange surfaces as shown by Process (I) in FIG. 82. Thereafter, grinding is effected to finish the wheel hub 14, which is subsequently assembled to complete a wheel support bearing assembly.